FIG. 1 is a diagram illustrating a wireless communication system. Referring to FIG. 1, a wireless communication system 100 includes a plurality of BSs 110a, 110b and 110c and a plurality of User Equipments (UEs) 120a to 120i. The wireless communication system 100 can include a homogeneous network or a heterogeneous network. In this case, a network where different network entities coexist, such as a macrocell, a femtocell, a pico cell, and a relay station, is designated as the heterogeneous network. The BSs are fixed stations that perform communication with a UE. Each of the BSs 110a, 110b, and 110c provides a service to specific local regions 102a, 102b, and 102c. In order to improve system throughput, the specific regions can be divided into a plurality of smaller regions 104a, 104b and 104c. Each of the smaller regions may be designated as a cell, sector or segment. In case of an Institute of Electrical and Electronics Engineers (IEEE) 802.16 system, cell identity is given based on the whole system. On the other hand, sector or segment identity is given based on the specific region where each BS provides a service, and has a value of 0 to 2.
The UEs 120a to 120i can generally be distributed, fixed or mobile in the wireless communication system. Each UE can perform communication with one or more BSs through an UpLink (UL) and a DownLink (DL) at a random time. The BS and the UE can perform communication with each other by using Frequency Division Multiple Access (FDMA), Time Division Multiple Access (TDMA), Code Division Multiple Access (CDMA), Single Carrier-FDMA (SC-FDMA), Multi Carrier-FDMA (MC-FDMA), Orthogonal Frequency Division Multiple Access (OFDMA) or their combination. Herein, the uplink means a communication link from the UE to the BS while the downlink means a communication link from the BS to the UE.
The BSs 110a, 110b and 110c communicate with the UEs 120a to 120i in a predetermined system bandwidth. If only a few regular system bandwidths are available for communication, the efficiency of frequency resource use is decreased. In this context, techniques for configuring system bandwidths other than regular system bandwidths for use in communication have been proposed in order to more efficiently use frequency resource. The techniques include carrier aggregation and tone dropping. In carrier aggregation, a wider system bandwidth than a regular system bandwidth is serviced by grouping a plurality of regular system bandwidths, whereas in tone dropping, a narrower system bandwidth than a regular system bandwidth is serviced by dropping a specific band from the regular system bandwidth. Accordingly, there exists a need for adapting a communication technique used in a regular system bandwidth to an irregular system bandwidth configured by carrier aggregation or tone dropping.